Method for producing tungsten in oxidic form from tungsten ore

ABSTRACT

TUNGSTEN IS RECOVERED IN OXIDIC FORM FROM TUNGSTEN ORES BY REDUCING THE ORE AT AN ELEVATED TEMPERATURE WITH A REDUCING AGENT, THEREBY FORMING TUNGSTEN METAL AND A SLAG WHICH IS SEPARATED TOGETHER WITH ANY OTHER METAL PHASES FROM THE TUNGSTEN. T HE TUNGSTEN IS SOLIDIFIED TO AN INGOT AND THEN CRUSHED TO FORM PARTICULATE TUNGSTEN METAL, THE TUNGSTEN BEING THEREAFTER SUBJECTED TO A DIGESTION AGENT TO CONVERT TUNGSTEN TO OXIDIC TUNGSTEN.

United States Patent 3,767,761 METHOD FOR PRODUCING TUNGSTEN IN OXIDIC FORM FROM TUNGSTEN ORE Ellis Kjell Ake Svanstrom, Nynashamn, Sweden, as-

signor to Rederiaktiebolaget Nordstjernan, Nynashamn, Sweden No Drawing. Filed Feb. 14, 1972, Ser. No. 226,255 Claims priority, application Sweden, Feb. 15, 1971,

Int. Cl. C01g 41/00 U.S. Cl. 423-53 4 Claims ABSTRACT OF THE DISCLOSURE The present invention refers to a method for producing tungsten in oxidic form from tungsten ore.

Conventional treatment of tungsten ore implies that the tungsten content of the ore is transferred into solution from which tungsten is precipitated out as ammonium paratungstate or tungstic acid. In order to obtain these products with a satisfactory purity, it may be necessary to redissolve and reprecipitate them once or several times. Certain impurities, e.g. tin or molybdenum, are particularly diflicult to separate in this manner. The purified product (ammonium paratungstate or tungstic acid) is reduced to tungsten metal powder by hydrogen.

The wet chemical method of producing tungsten powder, which at present is the only one used technically, is accompanied by several major disadvantages. Because most methods are specific for a certain type of ore, this implies a strong limitation in the selection of ore. Generally, wet chemical processes are complicated and divided into a considerable number of steps. This influences the economy of the process as well as the yield, which is generally low (about 85-90%). The presence of large amounts of impurities may decrease the yield even further. Because of high ore prices this is of great economical consequence.

The sensitivity to certain impurities, which is characteristic for wet chemical processing of tungsten ore, is a factor which has to be considered by the selection of the ore. It is further of importance for the process yield that the tungsten content in the ore be high.

In an attempt to simplify the processing of ore to form a high quality tungsten powder, certain producers have chosen to start with a highly pure scheelite ore. In doing so, they have succeeded in decreasing the number of process steps, lower the consumption of chemicals and increase the yield. These advantages have, at least partly to be paid for by a higher ore price. Also, these highly pure ores are getting less available, and the raw material coverage can be threatened. There is a need, therefore, of methods which will make possible processing of all kinds of ores and which are not dependent of high tungsten content in the ore in order to get good tungsten recovery.

It has been shown that this very important problem can be solved in a technically and economically satisfactory manner by melting the ore with one or more reducing agents, separating the slag from metal phases obtained as an ingot and containing essentially all the tungsten, crushing the ingot and treating the crushed material with acid and/or alkaline agents, whereby tungstem is transferred to and separated in oxidic form from the other alloying elements, whereafter tungsten in oxidic form is eventually reduced to metal.

Accordinng to the present method all kinds of ores can be processed in the same manner and ores with very low tungsten contents, e.g. 15-20% W0 can be processed without any appreciable decrease in tungsten recovery. According to the present invention the recovery is increased substantially also in comparison to what is normally possible with conventional technique.

The method according to the invention consists of a series of steps, each of which is known in its principle. The invention however, gives the unexpected effect that the various methods now applied can be replaced by a single process, which further gives the possibility to process low grade ores with a high yield. This is not possible with known technique.

The following steps are included in this process.

1) The ore is melted and reduced to metal, which is obtained as an alloyed ingot, and is separated from the slag.

(2) The ingot is crushed and digested whereby tungsten is transformed to oxidic form (ammonium paratungstate or tungstic acid).

(3) The oxide is eventually reduced, e.g. with hydrogen tungsten powder.

For the ore reduction reducing agents, such as ferro silicon, calcium silicon, magnesium-silicon, aluminium, silicon calcium carbide, carbon, or the like, are used. The most suitable of these are ferro silicon and aluminium because they make possible compact equipment and high recoveries. The reduction is suitably carried out in an arc furnace in a carbon crucible at a temperature of about 15002000 C., usually 1800- 2000 C. The temperature is dependant of ore composition, the type of ore and gangue, and of the reducing agent.

In this reduction step is separated the largest part of the ore components, which is of no economical interest, as slag. The metallic ingot formed in the reduction, gets the same general composition regardless of whether the ore is of scheelite or wolframate type. The essential influence of different ore types is on the iron content of the ingot. If this content should be too high for some ore a correction can easily be made by mixing with a suitable ore of low iron content.

Certain valuable by-products, which are common in tungsten ores, e.g. tin and bismuth are difficult to separate and to recover by conventional processing. They therefore lower the value of the ores in which they are present. According to the present invention these by-products are separated from tungsten in the reduction step, bismuth as oxide which can be recovered from the off-gases and tin as a separate metal phase on top of the tungsten ingot. Both products can be recovered and will contribute to a better process economy. The fact that certain by-products like tin, bismuth, arsenic etc. are separated in the reduction step, =Where bismuth and arsenic evaporate off in the form of oxides, is of great importance, because of the possibility to obtain a high quality tungsten material from impure ores.

The digestion of the crushed tungsten ingot can be carried out for example by melting with alkali nitrate and/0r sodium carbonate whereby tungsten is converted into a water soluble form. The ingot can also be treated with acids, like aqua regia, or with acids followed by alkali, e.g. sodium carbonate or hydroxide, in Water solution. Tungsten is normally precipitated as ammonium paratungstate (by adding ammonia), or as tungstic acid. These oxidic forms of tungsten can eventually be added directly to steel baths, where they are reduced to metal, or they can be reduced by hydrogen to tungsten powder.

In the upgrading of various tungsten ores, fractions can be obtained, which are not suitable for producing high quality tungsten products, e.g. because of too low tungsten content or too high content of certain impurities. The present invention gives a technical solution to the processing of such concentrates.

For certain ores it has been necessary to dissolve the ore concentrate and precipitate tungsten as synthetic scheelite in order to get full price for the ore. This causes additional costs as well as yield loss. Such a step is not necessary when the present invention is used.

One further advantage with the invention is that fractions with lower tungsten content than what is normally used, can be utilized. This means for instance that the upgrading of the ore does not have to be carried as far as is presently needed, which can result in lower upgrading costs and more important higher yield of tungsten.

Thus, according to the present invention, a gangue as well as certain impurities are separated by reducing the ore to metal. The subsequent digestion will therefore be technically substantially simpler, require less chemicals and less time, and also give a better yield than is possible with conventional technique. The invention has made it technically and economically possible to process poor and highly impure ores, which is of great value with the present relatively limited supply of rich tungsten ores.

What is claimed is:

1. A method of recovering tungsten oxide from tungsten ores which comprises:

forming a charge of said ore together with a reducing agent selected from the group consisting of ferrosilicon, calcium-silicon, magnesium-silicon, aluminum, silicon, calcium carbide and carbon,

heating said charge to an elevated reducing tempera- 4 ture range from about 1500 C. to 2000 C. to form a melt of slag and a bath of molten metal comprising tungsten, separating said molten metal from said slag and any separable metal phases present, solidifying said molten tungsten metal to form an ingot thereof, crushing said ingot, and then treating said crushed ingot by digestion in a liquid comprising a melt selected from the group group consisting of at least one of the digestion agents alkali metal nitrate and sodium carbonate to form tungsten oxide, or a liquid consisting of an acid solution to form a solution of tungsten which is thereafter precipitated as tungsten oxide by making the solution alkaline. 2. The method of claim 1, wherein the temperature ranges from about 1800 C. to 2000" C.

3. The method of claim 1, wherein the reducing agent comprises silicon.

4. The method of claim 1, wherein the reducing agent comprises aluminum.

References Cited UNITED STATES PATENTS 2,535,217 12/1950 Li et al 42353 3,256,058 6/1966 Burwell 121 X 2,993,755 7/1961 Redanz 423593 X HERBERT T. CARTER, Primary Examiner US. Cl. X.R. 

